1. Field of the Invention
The present invention relates to video communication systems in which individual frames may be grabbed for video display thereof.
2. Description of the Prior Art
Video communication systems in which the individual frames may be grabbed for video display are well known, such as the system disclosed in U.S. Pat. No. 3,740,465, or a system employing the Hitachi frame grabbing disc. These prior art systems such as the one disclosed in U.S. Pat. No. 3,746,780 are normally two-way request response systems requiring the user to request information by the dialing of a specific digital code which is uniquely assigned to each frame. However, such systems normally grab a group of frames for storage and then subsequently select the individual frame for display out of the group of grabbed frames as opposed to instantaneously selecting a single frame in real time. Furthermore, such prior art systems do not provide for real time updating of the grabbed video frame. In addition, some such prior art frame grabbing systems, such as the type disclosed in U.S. Pat. No. 3,397,283, are normally capable of only grabbing the next immediate signal in response to the provision of a starter signal or, as disclosed in U.S. Pat. No. 3,051,777, utilize a counter for frame location which must be reset to the beginning of a tape for video tape supplied information in order to locate a selected frame to be grabbed. These systems are not applicable in a real time frame grabbing environment. Similarly, other typical prior art frame grabbing systems, such as disclosed in U.S. Pat. Nos. 3,695,565; 2,955,197; 3,509,274; 3,511,929 and 3,582,651, cannot be utilized in a real time frame grabbing environment, such as the one in which the video information associated with the grabbed frame is capable of being continuously updated. Accordingly, presently available prior art frame grabbing digital systems familiar to the Inventor, other than commonly owned U.S. Pat. No. 3,889,054, are not capable of easily locating a frame to be grabbed in real time nor of being able to continuously update such a grabbed frame in real time.
Video communication systems in which the signal being transmitted is digitized are also well known. For example, U.S. Pat. No. 3,743,767 discloses a video communication system for the transmission of digital data over standard television channels wherein the digital data is transmitted in a conventional television scan line format through conventional television distribution equipment. However, such a prior art communciation system merely digitizes one television scan line at a time for distribution to a video display terminal on a bit-by-bit basis in a line, 84 bits of information being provided per television scan line. Furthermore, such a prior art system is not transmission selectable by every display terminal nor is the data for a displayable video row packed into a selfcontained pseudo video scan line information packet. Thus, there is no significant increase in the data transmission rate resulting from such a prior art video communication system. Similarly, U.S. Pat. Nos. 3,061,672 and 3,569,617 and German Pat. No. 2,307,414 are examples of other prior art video communication systems in which television signals are digitized without any significant resultant compression in data transmission time. Furthermore, these other prior art systems require special distribution circuitry. In addition, prior art video communication systems in which a digital television signal is transmitted do not sufficiently isolate the individual rows comprising a frame so as to provide satisfactory noise immunity between these rows nor is there satisfactory data compression in the transmission time of the video information in such prior art systems now satisfactory distortion compensation.
Furthermore, prior art row grabbing or frame grabbing video communication systems utilizing cable, for example, generally concern themselves with a single purpose cable channel for providing a video display of the "grabbed" data. Thus, although there are prior art "piggy-back" video communication systems, that is, systems in which a single line of digital data is transmitted simultaneously with normal television picture video, such as disclosed in British Pat. Nos. 1,163,016, issued Sept. 4, 1969; 1,132,303, issued Oct. 30, 1968 and 1,222,591, issued Feb. 17, 1971; and U.S. Pat. No. 3,927,250, issued Dec. 16, 1975; there are no satisfactory row grabbing video communication systems known to the Inventor employing a dual purpose cable channel for enabling the provision of conventional television as well as real time updateable row grabbed information in which every digital data packet of a piggy-back transmission is completely self-contained, such as in a pseudo video scan line, and includes all address functions required whereby the system is independent of the grabbable row transmission rate, nor are such systems which are known to the Inventor capable of maintaining phase lock to a single start bit.
These disadvantages of the prior art are overcome by the present invention.